A new procedure, "stopped-flow aggregometry", is being used to study the aggregability of platelets in diabetes. This uses the resistive-particle counter coupled to a stopped-flow system to measure the rate of disappearance of single platelets during the earliest seconds of aggregation. Both insulin dependent and insulin-independent adults will be compared to age, sex and weight-matched controls. ADP, epinephrine and thrombin will be tested as aggregating agents. The "shape-change" kinetics will also be analyzed in the diabetic and control groups. Scanning-electron microscope and resistive-counter measurements will be employed in these "shape-change" studies. One aim of the investigation is to determine whether evidence of hyperaggregability of platelets exists in patients who do not possess evidence of clinical disease.